Typhoid fever, although no longer a major public health problem in the United States, remains a major cause of morbidity and mortality in other areas of the world. Its recent recrudescence in developing countries of Latin America and its persistence in areas of developed countries in Europe and Asia represents a threat to American travelers and ultimately to public health in this country. Institution of curative therapy for typhoid fever depends on rapid diagnosis of infection with Salmonella typhi (ST), the cause of this disease. Unfortunately, serologic diagnostic assays for typhoid such as the Widal reaction currently in widespread use are not based on well-defined ST antigens and do not permit rapid early diagnosis of this disease. We have developed synthetic antigens containing ST O antigen polysaccharides conjugated to proteins for use in in vitro diagnostic assays, that react specifically with sera from immunized experimental animals and typhoid fever patients, but not with sera from unimmunized animals or normal human controls We have also previously cloned and expressed the ST 36 Wa porin in Escherichia coli (EC), characterized this porin as a strong immunogen during the evolution of typhoid fever, developed monoclonal antibodies (Mab) to the expressed porin and used these Mab to localize it to the ST surface. Our previous studies have thus provided a strong basis for developing rapid, inexpensive diagnostic assays for typhoid fever based on well-defined ST antigens that minimize use of resources. The specific aims of the project are: l) purify large amounts of ST O antigen from ST Ty2; 2) express and purify large amounts of recombinant ST 36 kDa porin from EC; 3) prepare ST antigen-protein conjugates based on these purified ST antigens and use them in immunodot assays and ELISA to quantitate IgM and IgG serological responses of patients with typhoid fever and controls: and 4) compare specificity and sensitivity of ST serologic assays based on synthetic conjugates with current serologic diagnostic assays for typhoid fever. The need for these assays is clear, in light of the recrusdescence of typhoid worldwide and the lack of adequate methodology to make an early diagnosis of typhoid. PROPOSED COMMERCIAL APPLICATIONS: The assays developed can be commercialized in countries that are involved in efforts to control typhoid fever. They can also be sold to institutions dealing with travel to developing countries, to the Health Services of Armed Forces, and other institutions with personnel operating in areas where typhoid fever is endemic. The total market for these type of diagnostic assays should be at least 15,000,000 units per year.